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C Standard Library <errno.h> C Standard Library <assert.h>

C Standard Library <ctype.h>

The C language <ctype.h> header file declares a set of functions to classify (and convert) individual characters. For example, isupper() checks whether a character is uppercase.

Introduction

C Standard Library ctype.h The header file provides some functions that can be used to test and map characters.

These functions accept int As a parameter, its value must be EOF or represented as an unsigned character.

If the parameter c meets the described conditions, these functions return non-zero (true). If the parameter c does not meet the described conditions, these functions return zero.

Library functions

The following lists the functions defined in the header file ctype.h:

Number	Function & Description
1	int isalnum(int c) This function checks if the character passed is a letter and a number.
2	int isalpha(int c) This function checks if the character passed is a letter.
3	int iscntrl(int c) This function checks if the character passed is a control character.
4	int isdigit(int c) This function checks if the character passed is a decimal digit.
5	int isgraph(int c) This function checks if the character passed has a graphic representation.
6	int islower(int c) This function checks if the character passed is a lowercase letter.
7	int isprint(int c) This function checks if the character passed is printable.
8	int ispunct(int c) This function checks if the character passed is a punctuation symbol character.
9	int isspace(int c) This function checks if the character passed is a whitespace character.
10	int isupper(int c) This function checks if the character passed is an uppercase letter.
11	int isxdigit(int c) This function checks if the character passed is a hexadecimal digit.

The standard library also includes two conversion functions that accept and return an "int"

Number	Function & Description
1	int tolower(int c) This function converts an uppercase letter to a lowercase letter.
2	int toupper(int c) This function converts a lowercase letter to an uppercase letter.

Character class

Number	Character class & Description
1	Digits Complete set of digits { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }
2	Hexadecimal digits Set { 0 1 2 3 4 5 6 7 8 9 Set { A B C D E F a b c d e f }
3	Lowercase letters Set { a b c d e f g h i j k l m n o p q r s t u v w x y z }
4	Uppercase letters Set {A B C D E F G H I J K L M N O P Q R S T U V W X Y Z }
5	Letters The set of lowercase letters and uppercase letters
6	Alphanumeric characters The set of digits, lowercase letters, and uppercase letters
7	Punctuation symbol characters Set ! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` { \| } ~
8	Graphic characters The set of alphanumeric characters and punctuation symbols.
9	Space character The set of tab, newline, vertical tab, form feed, carriage return, and space characters.
10	Printable characters The set of alphanumeric characters, punctuation characters, and space characters.
11	Control characters In ASCII encoding, the octal codes of these characters range from 000 to 037as well as 177(DEL).
12	Whitespace characters Including space characters and tab characters.
13	Letter characters The set of lowercase and uppercase letters.

C Standard Library <errno.h> C Standard Library <assert.h>